Accordian folded electrode assembly

ABSTRACT

An electrode assembly of an anode, a cathode and insulating separator material between the cathode and the anode characterized in that the entire anode, the entire separator and the entire cathode are laminated together in an accordian fold is disclosed. The assembly is useful in electrochemical cells.

FIELD OF THE INVENTION

The invention relates to an electrode assembly, a method for making theelectrode assembly and electrochemical cells in which the electrodeassembly is used.

BACKGROUND OF THE INVENTION

Various configurations of electrode assemblies consisting of an anodeand a cathode have been disclosed. The configuration and the arrangementof such electrode assemblies in a particular housing is important inthat the assembly and configuration impacts upon the (1) amount ofactive electrode material that can be included in each cell, (2)electrical performance, and (3) the ease of manufacturing.

A useful electrode assembly configuration is disclosed in U.S. Pat. No.3,663,721. Therein, an electrochemical cell is disclosed in which thelithium anode comprises a unitary and continuous length of zig-zagpleated lithium of a selected width. Individual cathode plates arepositioned between pairs of the pleated electrode. A separator is placedbetween the cathode and the anode to prevent electrical contact betweenthe anode and the cathode.

While this electrode assembly is useful, it is disadvantageous in thatit requires the manufacturing step of placing separate cathode platesbetween the zig-zag pleated anode. Also, such an arrangement requires aseries of electrical connections to be made between the various cathodeplates and the external electrical contact with the cathode therebyincreasing the opportunities for short circuits to occur.

SUMMARY OF THE INVENTION

The present invention provides an electrode assembly of an anode, acathode and insulating separator material between the cathode and theanode characterized in that the entire anode, the entire separator andthe entire cathode are laminated together in an accordian fold. Anaccordian fold comprises one or more "V" folds.

The electrode assembly of this invention is advantageous in that itavoids (1) the need for the manufacturing steps involved in makingseparate cathode plates and subsequently inserting such plates into thepleats of a zig-zag anode and (2) the need to make a series ofelectrical connections between individual cathode plates. Since thecathode is itself continuous, only one electrical contact need be madeto the cathode.

PREFERRED EMBODIMENTS OF THE INVENTION

In a preferred embodiment, the anode of the electrode assembly of thisinvention is a three piece laminate comprising, in the following order,

(a) a metal foil current collector support;

(b) a layer of a malleable anode-active material; and

(c) a layer of an insulating separator material.

In this embodiment, the electrochemical cell constructed with theaccordian folded electrode assembly of this invention has (1) decreasedinternal resistance and (2) better utilization of the anode-activematerial compared to electrochemical cells in which the anode is coatedon a metal grid current collector. This will be explained in greaterdetail hereinafter with reference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic drawing of the anode assembly.

FIG. 2 is a schematic drawing of a typical cathode assembly.

FIG. 3 shows the anode and cathode being laminated together prior to theaccordian fold.

FIG. 4 shows the laminate of FIG. 3 in an accordian fold.

FIG. 5 shows an electrochemical cell comprising an electrode assembly ofthe invention.

DETAILS OF THE INVENTION

Applicants will now proceed to describe the anode and cathodeconstruction, the separator and the technique by which they are broughttogether in a laminate structure and subsequently accordian folded. Inthis description of the invention, lithium anodes and MnO₂ cathodes areused. It will be recognized that the invention will work with mostelectrode assemblies using solid fuel.

The anode 11 in FIG. 1 is essentially a three piece laminate comprisedof lithium 12 coated on a 1 mil stainless steel foil current collector13. A portion of the stainless steel foil 13 is left uncoated andtrimmed to form the anode terminal 14. A separator 15 such as Celgard™4510 (available from Celanese) and/or non-woven polypropylene is rolledover the entire lithium anode 11. The separator is a porouselectrically-insulating material which prevents electrical contactbetween the anode and the cathode but allows movement of ions.

Other useful anode-active materials include any malleable anode materialsuch as alkali metals (Na and K), Li-Al alloys, Li-Si alloys, Li-Balloys and the metals of Groups Ia and IIa of the periodic table ofelements. Malleable anode-active materials are coatable on metal foil.Also, the separator can be coated onto the surface of the activematerial with considerable adherence of the separator to the anodelayer. Metal foils which can be used as the current collector andsupport include metals such as nickel, stainless steel, aluminum andtitanium.

While this embodiment of the invention is exemplified by having theinsulating separator placed over the anode, it is clear that theinvention works equally well when the separator is placed over thecathode. In any case, a small excess of separator is left relative tothe ends of the electrode. The total length and thickness of the anodewill be dictated by the fuel loading requirements of the electrochemicalcell or battery specification under consideration.

The cathode is a laminate as shown in FIG. 2. It is made with MnO₂. TheMnO₂ cathode 1 comprises a stainless steel grid current collector 22coated on one or both sides with a mixture of MnO₂, carbon and Teflon™23. A small portion of the stainless steel current collector is leftuncoated and shaped at one end to function as a cathode terminal 24.

The wide variety of cathode-active materials which would be useful inthe electrode assemblies of this invention include the various forms ofpolyfluorocarbons, i.e. (CF_(x))_(n) wherein x<4 and n is someindeterminate large number, FeS₂, FeS, CuO and Bi₂ O₃.

A complete electrode assembly is shown in FIG. 3. It is made bypositioning the cathode 1 on top of the separator 15 attached to theanode 11 so that the cathode terminal 24 and the anode terminal 14 areside by side but are not in electrical contact. The cathode, in thisembodiment of the invention, is about one-half the length of the anode.The entire anode 11 is then folded over the entire cathode 1 to form alaminate structure in which the cathode 1 is sandwiched between thefolds of the anode 11.

Next, the complete electrode assembly of FIG. 3 is then accordian foldedmanually as shown in FIG. 4. The accordian folded electrode assembly ofFIG. 4 is a series of connected "V" folds. The accordian foldedelectrode assemblies of this invention comprise two or more "V" folds.The length of each leg in the fold and the number of folds and legswill, of course, be determined by the dimensions of the container inwhich the electrode assembly is to be inserted. Obviously, electrodeassemblies having more than two "V" folds or four legs are possible,depending upon the fuel loading requirements of the intended powerapplication and the specific anode and cathode materials used.

One method for folding the electrode assembly of this invention,referring to FIG. 3, is to make sequential folds beginning at the endaway from the contacts 14 and 24. As each fold is made, the loose endsof the separate components are thus free to shift enough to reducestresses and strains at the fold thereby preventing pinching, cracking,breaking, delamination, shorting, or the like.

After checking for internal electrical shorts with an ohmmeter, theelectrode assembly is made into an electrochemical cell or battery byfirst inserting the assembly into a container 25 such as shown in FIG.5. An electrolyte comprising, for example, a solvent mixture of apropylene carbonate and dimethoxyethane or butyrolactone anddimethoxyethane with a lithium salt such as lithium perchlorate orlithium tetrafluoroborate is added to the container 25.

The electrode assembly is inserted in the container so that electrodeterminals 14 and 24 protrude upward forming a complete electrochemicalcell or battery. The cell can be sealed with a cap if desired. Such capsand methods of sealing the cap to the container are well known in thebattery art.

In the accordian folded electrode assembly of FIG. 4, electrical contactbetween each leg of the anode is achieved when the legs of the assemblyare pressed together and inserted into the container of FIG. 5. Thiselectrical contact is achieved through the physical contact of the metalfoil collector current collectors 13 of the anode assembly 11. Thiselectrical contact between each leg of metal foiled back anode decreasesthe internal resistance of electrochemical cells because electrons havea shorter path to travel to reach the anode terminal compared to anodesand electrode assemblies having a different configuration.

Moreover, the anode construction of FIG. 1 facilitates greaterutilization of the anode-active material since substantially all of theanode-active material is in direct electrical contact with the metalfoil current collector. This is in contrast to metal grid collectors inwhich much of the anode-active material is only indirectly in electricalcontact with the grid current collector.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:
 1. An electrochemical cell having an electrolyte and anelectrode assembly comprising a lithium anode, a MnO₂ cathode and aninsulating separator material between the anode and cathode, wherein(a)the anode and the separator forms a three piece laminate comprising inthe following order(i) a metal foil current collector support; (ii) alayer of lithium and (iii) a layer of an insulating separator material;(b) the anode is about twice the length of the cathode; (c) the anode isfolded in half; (d) the cathode, comprising a metal foil currentcollector coated on both sides with MnO₂, is sandwiched between the foldof the anode to form the electrode assembly; and (e) the entireelectrode assembly is laminated together in an accordian fold.
 2. Anelectrode assembly of an anode, a cathode and insulating separatormaterial between the cathode and the anode wherein(a) the anode is abouttwice the length of the cathode, the anode is folded in half and thecathode is sandwiched between the fold of the anode and the entireassembly is accordian folded and (b) the anode and the separator is athree piece laminate comprising, in the following order,(i) a metal foilcurrent collector support; (ii) a layer of a malleable anode-activematerial; and (iii) a layer of the insulating separator material.
 3. Theassembly of claim 2 wherein the active cathode material is selected fromthe group consisting of polyfluorocarbons, FeS₂, FeS, CuO, MnO₂ and Bi₂O₃.
 4. The assembly of claim 2 wherein the anode-active material islithium and the cathode comprises MnO₂ as the active material.
 5. Theassembly of claim 2 or 4 wherein the cathode is laminated to a stainlesssteel grid current collector.
 6. An electrochemical cell comprising anelectrolyte and an electrode assembly of claim 2 or
 4. 7. Anelectrochemical cell comprising the electrode assembly of claim 2 or 4and an electrolyte comprising a solvent mixture of (a) propylenecarbonate and dimethoxyethane or (b) dimethoxyethane and butyrolactoneand a lithium salt.
 8. The assembly of claim 2 or 4 wherein the cathodecomprises a metal foil current collector coated on both sides with theactive cathode material.